Cotton
is a temperature sensitive crop. At the time of sowing if temperature is low it
causes poor germination and if temperature is high it causes poor plant growth
and etiolation. High temperature is favorable for insect and pest attack and it
causes damage to boll.

During summers when the temperature is high it causes diapause.
These diapauses are ended by temperature fall. As a result of high temperature
some of the bollworm population becomes dormant and there is a negative
feedback mechanism due to the synchronization of the adults during autumn.

 

 

Our
research has also confirmed that the offspring of parents which had experienced
summer diapause had higher survival rates compared to those whose parents had
not experienced summer diapause, and they weighed significantly more than those
from non-summer-diapausing parents under normal rearing conditions.

 

 

Moisture
was not a limiting factor at Guttenberg (New Jersey) and Vicksburg
(Mississippi) (Fig. 4a, b) as a result of abundant rainfall. At these
localities, the population growth of P. solenopsis was mainly affected
by temperature; the variation of GIW corresponded with TIW (the weekly
temperature index), particularly with a marked cold stress value of 26 in winter
in Guttenberg (Table 2). The variation in TIW and MIW (the weekly moisture
index) at Miami (Florida) (Fig. 4c) suggested that high summer temperatures and
excessive moisture in autumn were likely to restrict population growth,
indicating that areas with extremely high rainfall were unfavourable for
serious infestation by P. solenopsis. In the western and southern
U.S.A., there is usually only a little, asymmetrical natural rainfall each
year, so that temperature and soil moisture together affected the seasonal
population growth of P. solenopsis (Fig. 4d, e). At Las Cruces

(New
Mexico), low MIA accompanied by a cold stress value of 39 limited the
population growth of P. solenopsis (Table 2). In the northwestern
U.S.A., restricted natural rainfall and an extremely cold winter limited growth
and reproduction of the mealybug. The mealybug can colonize different
microhabitats on the plants to ensure its survival. It can occur on the roots
or the crown of its host, so avoiding very hot and dry and/or very cold conditions
to some extent. Lack of soil moisture might directly impact this mealybug if it
is restricted to roots in the upper layer of soil. As was found for the U.S.A.,
the combination of low precipitation and cold temperatures reduced the
potential survival and colonization of P. solenopsis in Asia dry stress

(Fig.
9) and cold stress (Fig. 10). The other large cotton-growing areas in China
(Huang-Huai-

Hai
regions and Changjiang River areas), and the cotton growing areas of Pakistan
and India, were all identified by CLIMEX as ‘highly suitable’ habitat for P.
solenopsis. The areas in Pakistan and India are already infested (Muhammad,
2007; Nagrare et al., 2009) but not the areas in China (Wang et al.,
2009). With the mealybug established in all these areas, the forecast losses in
cotton yield in 2008/2009 would be 1.4 million tons in China, 1.12 million tons
in India and 0.48 million tons in Pakistan (Table 3). (Yanping Wang, 2010)

 

 

Climatic conditions can affect boll weevil populations and the
persistence of kaolin particles on plants (Showler 2007). The survival of insects
in cotton agro ecosystems is influenced by high temperature and low humidity
(Ramalho and Silva, 1993), and the persistence of kaolin particles is also reduced in
environments that experience high levels of precipitation (Lo Verde et al. 2011). In
our study, the temperature, relative humidity
and weekly rainfall were favorable to the pest
population development and not hampered
spraying with kaolin.

The
tallest plants, lower number of bolls and lowest cotton-seed yield of the
control plot may be attributed to the higher percentage of
oviposition-punctured squares observed in this
treatment. On the other hand, the smaller plant
height, larger number of bolls, and higher cotton-seed

yields of the cotton plots sprayed systematically with endosulfan,
either weekly or from the 10 % economic threshold, can be attributed to the
lower percentage of oviposition-punctured squares observed in these treatments.
There has been found a negative relationship describing cotton-seed yield and
non-attacked bolls as a function of oviposition-punctued squares by boll weevil

(Bevers and Slosser 1992, Slosser 1993, Showler et al. 2005). (C. A. D. Silva • F. S. Ramalho)

 

 

Mortality of developing immature weevils in squares can be quite high due to predation,

parasitism and high temperatures, but more than 50 percent will usually

emerge as adults (Fenton and Dunnam, 1929; Smith, 1936; Bacheler et al., 1975;

Chesnut and Cross, 1971). These newly emerged weevils will mate and begin

ovipositing after five to eight days, unless they are subjected to cool temperatures or

diapause-inducing conditions (Fenton and Dunnam, 1929; Roach, 1979; Cole and

Adkisson, 1981). Intedield movement and long range migration can occur in any surruner brood of weevils (Isely, 1926; Roach eta/., 1971; Roach and Ray, 1972). Most mass movements

of weevils apparently occur when fields become heavily infested and few oviposition

sites remain (Fenton and Dunnam, 1929; Fye and Bonham, 1970). The direction

of movement seems to be random and possibly wind-aided. Migrating individuals are

known to move up to 45 miles (Davich et a/., 1970; Beckham and Morgan, 1960). Temperature, moisture and photoperiod are important factors affecting the pink

bollworm. Termination of diapause primarily is a function of temperature and moisture.

Temperatures in excess of 59F ( 15C) are necessmy for initiating pupation of overwintering

larvae. Contact moisture or high relative humidity enhances survival and

pupation, especially at higher temperatures. A temperature of about 72F (22C) and

contact moisture appear to be most optimum for survival and the highest rate of pupation

(Watson et al., 1973). During the growing season moth activity is adversely

affected by unusually high temperatures, and longevity and oviposition are reduced

when temperatures exceed 95F to 104F (35 to 40C). Winter mortality of diapausing

Jm·vae generally is high and areas with cold, wet conditions m·e most detrimental to